Yup, you have to fix many kind of engines (any kind of problems, from electrical ones up to crankshaft failures, which involves disassembling the entire engine), drivetrain probles, braking system problems, body and paint, etc...

The only problem is, the broken parts show up as rusty parts. Brand new parts are shiny and perfect, old/broken ones are 100% rusty, so even though sometimes you have to discover what's wrong with the car, by finding the rusty parts, you can solve that problem quite easily. Some old cars are very rusty, so at least on these ones finding the bad parts involve using tools, making a test drive...but it's quite addicting.

You can also unlock a private garage and buy cars on auctions, all of them quite broken, so this bit is kinda like Street Legal Racing, a nice touch.